US8253622B2 - Device and method for the improved directional estimation and decoding by means of secondary radar signals - Google Patents

Device and method for the improved directional estimation and decoding by means of secondary radar signals Download PDF

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US8253622B2
US8253622B2 US12/918,836 US91883609A US8253622B2 US 8253622 B2 US8253622 B2 US 8253622B2 US 91883609 A US91883609 A US 91883609A US 8253622 B2 US8253622 B2 US 8253622B2
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antenna elements
signal
matrix
analog
linear amplifier
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US20110001659A1 (en
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Hermann Hampel
Ulrich Berold
Christoph Reck
Lorenz-Peter Schmidt
Jochen Weinzierl
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IAD Gesellschaft fuer Informatik Automatisierung und Datenverarbeitung mbH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
    • G01S13/78—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe
    • G01S13/781—Secondary Surveillance Radar [SSR] in general
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/02—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using radio waves
    • G01S3/74—Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals

Definitions

  • the invention concerns, according to patent claim 1 , a device for the improved directional estimation and decoding by means of secondary radar signals and, according to claim 10 , a method for its implementation.
  • Primary radar systems are radar devices, applying the radar principle exclusively and directly, i.e. direct (passive) echoes of previously transmitted high frequency pulses are analyzed.
  • the term serves to distinguish from secondary radar systems, a method, in which echoes generated by the detected objects are actively used. In practice often a combination of both methods is used (e.g. in flights safety with ground station radar).
  • Primary radar equipment does not expect the object to generate active signals, so that it can be detected. This is used, for example, in ensuring flights safety, because it must be possible to detect planes also in the case of damaged radar transponder. In case of interference in the used frequency, primary radar equipment can easily be adjusted to other frequencies. In secondary radar equipment, such a change may be successful only if performed also for the objects to be detected.
  • the primary radar can find the values only by the reflected echo (e.g. direction, distance and speed), while the receiver in secondary radar can integrate additional data in its response (e.g. marking).
  • Primary radar equipment require significantly higher transmit power than comparable secondary radar systems in order to achieve equal range.
  • the principle of secondary radar is a procedure for detecting the position by measuring time, which unlike normal radar equipment does not work with the energy reflecting in the target, i.e. with the passive echo of the target and on the board of the target, an active response unit (transponder) is located.
  • targets respond actively to the received radar signal by sending a response with the same or another frequency.
  • the radar pulse is received by an antenna and it transmits a characteristic “echo” by the same antenna.
  • This response can be a specific modulation or a data package.
  • a great advantage of secondary radar systems to primary radar systems is its apparently greater range, as well as the ability to identify the target. With primary radar, reliable information on the direction, altitude and distance of the target is received, and this occurs completely independently of the target.
  • Secondary radar finds additional information, such as marking, identification and also the altitude of the target. In any case, support by the target is necessary. If there is no such support, for example, if the transponder is defective, the secondary radar cannot work and this flying object is not detected. That is why most secondary radar systems operate in combination with a primary radar system.
  • the international standard Mark X was formulated (this system was quite simply structured and worked at a frequency of 950 MHz to 1150 MHz on 12 different channels with an interval of 17 MHz) and it was extended many times until 2008, as now it is a basis for civilian use of the secondary radar in aerial safety.
  • DABS Discrete Address Beacon System
  • the secondary radar system consists of two devices: an interrogating device (interrogator) and a response device (transponder).
  • interrogator interrogating device
  • transponder response device
  • interrogator In air traffic interrogators are partly ground stations, partly interrogators mounted on airplanes.
  • the interrogator sends independently of the type of modulation (so called mode) a question, encodes with different pulses. These pulses are received by the transponder and are evaluated. According to the contents of the question, a reply is generated, which is encoded again and which is transmitted.
  • the distance between the interrogating device and the responding device can be calculated. Because of delays caused in the transponder due to encoding and decoding, this calculation of remoteness is correct only when the additional time of delay is known.
  • DPSK pulse modulation with differential phase shift keying
  • uplink path interrogation from ground station high to the airplane
  • the response in most modes lasts for 20.3 ⁇ s, consists of 2 to 15 pulses with pulse duration of 0.45 ⁇ s ( ⁇ 0.1 ⁇ s) each, possesses only one spare value of 4096 different codes for identification due to the used four-position octet code and is transmitted at frequency 1090 MHz.
  • DPSK differential phase shift keying
  • a feature of a Mode S transponder is the so called squitter mode, where the transponder regardless of interrogation sends at regular intervals for example the GPS position and identification (ADS-B Automatic Dependent Surveillance-Broadcast).
  • a secondary radar system (SSR) is known, in which there is no need for a rotating antenna for receiving the response, requested from the transponder.
  • the procedure for identifying and/or determining the location of an airplane is characterized by the fact that first, a pair of pulses for interrogation is transmitted in a band of the transponder field, which determines the position of the transponder being searched and which is used to suppress all other signals from other transponders, a pair second of pulses for interrogation of the transponder being searched is transmitted, at which the transponder being searched is preferably interrogated when the other transponders are suppressed, and the response sent by this transponder is received for identification and/or detection of location.
  • An alternative method of the invention consists of the fact that the time relationship between the pulses of the first pair of pulses changes in stages, so that the predetermined region is passed through stages, in which it is preferable that the region is passed in a series of bands in one direction, and then in the same way in the other direction.
  • a device according to this method is in a first alternative characterized with first and second antennas placed at the end of the region and available for each other and thus facing each other, so as to transmit a certain pair of first pair of pulses for interrogation, and there is also a third antenna, which is placed on the edge of the region, and the third and the first or the second antenna are located so as to transmit certain pairs of pulses for suppression.
  • a further alternative is characterized by the fact that the first and second antennas, which are located on the edge of the region, are positioned to each other and at such a distance so as to transmit certain pairs of the first pair of pulses for interrogation, and the third and the fourth antennas are located on the edge of the predetermined area so as to transmit certain signals for suppression.
  • the third antenna can be located in such a way that the response from the transponder being searched is received by it; it is possible that at least three of the antennas are located so that the respond from the transponder being searched is received to determine its position within the predetermined region.
  • the position of the airplane can, as described above, be determined by the frame pairs of pulses of the response of the transponder, but more accurate position of the transponder can be obtained, if each antenna receives the response of the selected airplane and for determining the position of the airplane a tripartite procedure is used. Expansion is obtained by providing a fourth antenna used along with other antennas for sending suppressing pulses. Thus, a greater accuracy of suppression is achieved, whereupon the characteristic of insensitivity of the original transponders leads to a relatively low resolution. This problem is minimized by the use of dual suppression procedure, in which initially all located on a given hyperbola transponders, and then all the transponders at the airport are suppressed. When initially suppressed transponders are free again (i.e.
  • the signals coming from the response stations to be obtained from a second antenna located on the airport at a good distance from the interrogation antenna, which forms a sharply converging antenna, which also scanned the airport and the transmissions generated by these two antennas shall be directed in such a way that their zone of intersection cover each point of the airport sequentially, and thus, by the means of the zone of intersection to determine the position of the plane.
  • Improving in accuracy with regard to detection of location is achieved by receiving, on one hand, response signals sent by the response stations for response from the second antenna located far apart from the interrogation antenna located on the airport, which, however, forms sharply curved funnel, and which inspects the airport, and whose response signals are directed by the two antennas through the funnel for transmission, so that the zone of intersection detects each point of the airport; thus, by the means of such zone of intersection, the position of the airplane can be determined, and on the other hand, the response signals coming from the response stations are received by two or more circularly transmitting antennas distributed on the airport and located at a distance from the interrogation antenna, and the position of the respective airplane is calculated using the hyperbola location procedure.
  • a system for preventing collisions with finding the position in its home station which by SSR interrogations and responses determines the positions of its home station and the positions of the other stations.
  • the starting position of its home station is determined by active measuring the distance to the transponders of the other stations, whose subsequent responses to interrogations of its home station are free of interference, caused by overlap of the responses.
  • interference must be described as a block.
  • unblocked responses are chosen and their delay with respect to interrogations is a measure of the direct distance from the other stations to the home station.
  • the home station sends a short signal with repeated interrogations from mode A and mode C and correlates them with the received responses. If the transponder responds without blocking to more than one station, then that station which is best situated to determine the exact position is selected. It is not necessary to follow the adjustments of its own position. All interferences of the existing ATCRBS mode from interrogations from of its home station and responses to them are only superficial and can be ignored as a whole.
  • the positions of the home and the other responding stations are determined in a trigonometric way by the measured distances and the bearing differences, and from the time differences at the arrival of the interrogations from the SSR station and from the next unblocked responses to these interrogations from the above mentioned identified transponders from the other stations. Once the position of the home station is determined through active transmissions combined with passive data then the relative positions of other transponder stations are determined passively.
  • a device for control at the airport is used at radar devices, which have cluster sensitivity to ground, which is low, and these radar devices can simultaneously control the airspace and ground space at the territory of the airport.
  • a device for detecting obstacles and controlling movements on and over the territory of the airport by sensors is territory implemented, where one sensor is a radar device with multiple antenna elements that are placed on the curved surface of the mounting of the antenna and they are run one after another at intervals, whereupon the antenna elements are arranged in circles and the first circle and the second circle form a plane, whereupon the planes formed by the circles stand vertically to one another and whereupon the antenna elements located in one horizontal plane are intended to control the airspace and to determine the altitude of flying of taking off or landing flying objects, respectively by ROSAR principle and there is another sensor which is a ROSAR radar device, which by rotating the antenna forms a synthetic aperture, whereupon the device is positioned on the take off and landing band.
  • elements of ROSAR radar device are controlled and turned off at intervals one after another.
  • an antenna element situated in a horizontal plane the control of the territory of the airport is implemented, and by antenna elements located in a vertical plane, the control of the airspace of the airport is implemented.
  • using the device it is possible to determine the altitudes of flying of landing or taking off flying objects.
  • a secondary radar system may not be placed on the ground, either.
  • a passive system to prevent collisions is known and also a procedure by which, in an equipped with GPS surveillance airplane, responses from the airplanes located in the control zone, sending those to the ground station, are assessed.
  • the signals at the output of the analog-to-digital converter in the complex main band are fed to a single digital signal processor, which establishes whether a valid signal is received from the mode A or C and which filters all signals that are not related.
  • Lying on the output DSP signal which includes all valid information from Mode A or C, namely the relevant identification of the target transponder and altitude data, is supplied with the own GPS data via USB cable to an onboard laptop, PDA or notebook located on the surveillance airplane.
  • the assessment of the direction, performed in the laptop, PDA or notebook, that is based on GPS data and the responses from the targeted airplanes, located in the range of surveillance may be done for example by the procedure for assessment ESPRIT, MUSIC (Multiple Signal Classification), WSF (Weighted Subspace Fitting) and the result may be presented on a screen attached to the pilot's leg.
  • the accuracy of assessment of direction depends on many factors, such as the signal-to-noise ratio SNR, number of measurements, number of signals to be received (responses), the angular resolution between the different signals, the deviation of the antenna response from the angle, the deviation of the ideal antenna group (generation error) and the possibility of systematic calibration.
  • radiobased location systems based on secondary radar signals are known.
  • special reception systems are used for the purpose of assessing the direction and, on the other hand, special systems for decoding the secondary radar signals.
  • no secondary radar device is present, where the disadvantages of hardware used, such as connected antenna elements, different impedances of the reference point, deviating distances between antenna elements, production and assembly tolerances, etc. are taken into account.
  • an object of the present invention to implement a radiobased location system in a way that allows for improved assessment of the direction, including decoding based on secondary radar signals. Further, location system must provide opportunity of expanding on the purpose of determining the position.
  • a device for the improved directional estimation and/or decoding by means of secondary radar signals which comprises:
  • this problem is solved by a device for determining the position and/or decoding based on secondary radar signals in accordance with patent claim 2 ; this device comprises:
  • FIG. 1 Block circuit diagram of a first embodiment
  • FIG. 2 Circuit diagram of the antenna elements
  • FIG. 3 RMSE through the carrier offset
  • FIG. 4 The results of the simulated antenna coupling between antenna elements
  • FIG. 5 RMSE for the standard deviation of the absolute values of amplification of input levels, normalized to its nominal gain
  • FIG. 6 RMSE for the standard deviation of the phases of input levels, normalized to ⁇
  • FIG. 7 RMSE for the assessment of the direction with a parameterized simulation model, based on values measured by the hardware through the carrier offset
  • FIG. 8 Histogram of errors in the assessment of the direction with ESPRIT, based on 2000 received ADS-B messages
  • FIG. 9 Histogram of errors in the assessment of the direction with NC Unitary ESPRIT, based on 2000 received ADS-B messages
  • FIG. 10 Schematic system picture for determining the position based on the assessments of the direction from several groups
  • FIG. 11 The error in the assessment of the direction to the angle of incidence for ESPRIT based on 14 222 ADS-B messages with and without calibration, and
  • FIG. 12 Histogram of errors in the assessment of the direction for ESPRIT based on 14 222 ADS-B messages with and without calibration.
  • the secondary radar at 1090 MHz is used for identification purposes and transmission of common data for the flight between the flying objects, ground vehicles and the safety of flight.
  • the secondary radar at 1090 MHz is used for identification purposes and transmission of common data for the flight between the flying objects, ground vehicles and the safety of flight.
  • works are done on the task of application based on a concept of multilateration in the range of the determination of the position.
  • ISI intersymbol interference
  • An antenna array for estimation of direction can improve the effectiveness of multilateration system and replace it for short distances.
  • FIG. 1 shows the block circuit diagram of the first form of implementation of the equipment for estimation of direction and/or decoding of the secondary radar signals, which comprises:
  • the second linear filter F 2 shall be connected to a third linear amplifier V 3 to amplify the signals from the low level, for which the second analog-to-digital converter AD 2 is connected.
  • the second analog-to-digital converter AD 2 with the corresponding amplifier is intended to increase the dynamics of the system, as the needed dynamics is higher than the dynamics of the present analog-to-digital converter.
  • the antenna array A consists of at least three omnidirectional antenna elements AE, which, except of MUSIC, are formed as a linear array A with equal distances between the antennas of half a wavelength.
  • the antenna element AE is equipped with a reflector in the form of half way tube with a diameter of half a wavelength, serving for both adapting and decoupling.
  • antenna elements AE are formed as frame antennas on a bearing plate and the rear side of the holder has a metal surface for shielding.
  • a radioreceiver FE is connected to them (e.g. for reception of GPS or Galileo signals) and/or an interface switching TZ connected via a cable (for example, to connect an Ethernet connection).
  • one of the signal processors FPGA generates the first and second clock signals CK 1 , CK 2 as time for the mixer M and analog-to-digital converters AD 1 , AD 2 and a coherent analog-to-digital signal processing is done in the processing unit CPU connected to the signal processors FPGA, which collects data DD of all antenna elements AE and performs estimation of the direction by a method based on a subspace.
  • MUSIC Multiple Signal Classification
  • ESPRIT Estimation of Signal Parameters via Relational Invariance Techniques
  • NC Non-Circular Unitary ESPRIT
  • Matrix Pencil is used.
  • MUSIC Multiple Signal Classification
  • ESPRIT Estimation of Signal Parameters via Relational Invariance Techniques
  • N Non-Circular Unitary ESPRIT
  • Matrix Pencil is used.
  • the directions of falling are not directly calculated, but the so-called pseudospecter from which the directions of falling are determined is found.
  • mixer M mixing takes place in the complex equivalent main band, as well as subsequent depth filtration.
  • ADS-B messages that contain the position of the airplane established by fixed location by a satellite (Global Position System GPS) on board are used as a reference.
  • the method according to the invention is particularly characterized by the use of estimation of the direction and/or estimation of the altitude.
  • the information on the position and the data of movement are assessed in the processing unit CPU, contained in the signal processors FPGA as a positional information system for detection/processing.
  • Signal processor FPGA after setting a defined time or when reaching a predetermined distance, provide one or more position data and send them in a package (of data) to the processing unit CPU.
  • the data package shall be saved in the processing unit CPU at certain intervals circularly/cyclically.
  • the processing for finding the angle of falling first takes place in the common processing unit CPU.
  • the above values for intermediate frequencies, the sampling frequencies, widths and amplifying factors are preferably used, but there are also free parameters with regard to system optimization.
  • the control signals and a clock from the mixers and from the analog-to-digital converters between separate channels must be synchronized.
  • X (M ⁇ N) describes the reception matrix
  • a (M ⁇ d) represents the matrix for forming the beam (steering matrix). If the distance between antenna elements is half a wavelength, then
  • A [ 1 1 ... 1 e j ⁇ ⁇ sin ⁇ ( ⁇ 1 ) e j ⁇ ⁇ sin ⁇ ( ⁇ 2 ) ... e j ⁇ ⁇ sin ⁇ ( ⁇ d ) ⁇ ⁇ ... ⁇ e j ⁇ ⁇ sin ⁇ ( M ⁇ ⁇ ⁇ 1 ) e j ⁇ ⁇ sin ⁇ ( M ⁇ ⁇ ⁇ 2 ) ... e j ⁇ ⁇ sin ⁇ ( M ⁇ ⁇ ⁇ d ) ] .
  • Matrix B (d ⁇ N) contains the symbols for transmission.
  • the angles ⁇ n with d ⁇ ⁇ 1, 2, . . . , d ⁇ describe the angles of the received signals.
  • the matrix N presents the additional white noise.
  • This reception model defines a group of antennas A of ideal isotropic antenna elements AE, followed by coherent analog and digital signal processing, where the algorithms for assessment of the direction must virtually work with a group which has connected antenna elements, different impedances of the reference point and deviating distances between the elements. Tolerances of implementation and installation lead to different amplifications and differences in the phases (respectively variable number of noises) in the analog input levels. These shortcomings of the hardware in use must be taken into account in the reception model. Connecting the antenna elements, different impedances of the reference points and various amplifications, respectively, phase course can be represented by the coupling matrix C (M ⁇ M)
  • FIG. 2 shows a group/array of four antenna elements with connecting factors c mn , forming an ideal antenna group on a model close to the reality.
  • the coupling matrix C in the procedure according to the invention is preferably found by calibration, which is preferably implemented by self-structure analysis.
  • the ideal vector of the beam formation can be found, as far as C is known. Otherwise, C can be found in case of sufficiently uniformly distributed ideal vectors for beam formation and their corresponding observed vectors of beam formation.
  • the vector for beam formation is estimated by dividing the dominant eigenvector (main eigenvector) A estim to the covariant matrix R xx that is formed by a limited number of reception values.
  • the main eigenvector is compared with its corresponding ideal vector for beam formation A.
  • J. Pierre and M. Kaveh “Direction-Finding Using a Laboratory Experimental Array Testbed”, 5th ASSP Workshop on Spectrum Estimation and Modeling, pp. 114-118, 1990 and “Experimental Performance of Calibration and Direction-Finding Algorithms”, IEEE Int. Conference on Acoustics. Speech and Signal Processing, vol. 2, pp. 1365-1368, 1991, this results in the minimization problem:
  • the respective eigenvector z min is used as an estimate of vector g.
  • the coupling matrix C for the case of negligible antenna connection is given by equation (7), in the other case by equation (10). If the calibration is done by multiple reception vectors, i.e. multiple vectors for beam formation, then optimization the coupling matrix C by several equations (6), respectively. (8), is carried out.
  • multiple sources to identify the corresponding positions/angles of falling can generally be used. Relevant information can be found, for example, by the ADS-B messages or by additional information for the airspace control (e.g. primary radar) or by measuring flights (with the appropriate display of data).
  • a unitary matrix is used, where the calibration procedure may not be necessary.
  • calibration costs and costs for storage of relevant data are eliminated. This simple way of working can be used for example in cases where the estimation of the direction has low accuracy.
  • Knowing the matrix F is not a prerequisite for the use of algorithms for the estimation of the direction of the basis of equation (4) and the reception model present in it, and it is used for modeling of the compensation of the frequency of medium, respectively the resulting phase division in order to compare the algorithms with each other and their productivity.
  • NC Unitary ESPRIT is then examined for related ESPRIT, since it is limited to signals that concentrating its modulation alphabet to a few degrees of the complex plane. This special case is fulfilled by all purely amplitude modulated signals, as well as by SSR signals.
  • the used antenna group A consists of four omnidirectional antenna elements AE at a distance of half a wavelength.
  • the distance of interference (SNR) is set at 40 dB and 50 values from the review for one estimation are used.
  • the angle of falling is randomly selected between 80° and 100°.
  • FIG. 3 shows that the accuracy of estimation cannot be decreased to the compensation of the medium of 10 kHz. If this value is crossed, then the accuracy with all algorithms, except with NC Unitary ESPRIT is obvious, and a maximum RMSE value is reached at 1 MHz. This maximum is almost equal for MUSIC and Matrix Pencil and it is between 30° and 40°. In ESPRIT, the value is clearly lower at about 6°. NC Unitary ESPRIT shows almost complete lack of being influenced and thus can be described as an optimal algorithm for assessment of the direction of an individual SSR signal.
  • connection c neignb in [dB] given in the description of the axles (in terms of power) is defined between two adjacent antenna elements AE.
  • the analog input levels connected to the antenna elements AE have different complex amplification factors.
  • the influence of the different absolute values of amplification is presented in FIG. 5 .
  • the nominal amplification of the input levels and the distributed compensation for amplification is characterized by an increasing standard deviation.
  • MUSIC is the least reliable and loses lost with the standard deviation 0.1 in terms of accuracy of the estimation.
  • NC Unitary ESPRIT starts to lose accuracy from 0.1 and ESPRIT and Matrix Pencil—from 0.3. However, breaking the accuracy of the estimation is not great. All algorithms without MUSIC exceed RMSE of 1° slightly less than 0.4.
  • results with non-homogenous phase course show in the same RMSE results for all algorithms except MUSIC. All algorithms are similar with a different phase course. The accuracy of the estimation is worsened at standard deviation of 10 ⁇ 4 ⁇ .
  • the construction of measurement being used is based on ULA from six single pole elements at a distance of half a wavelength (this is not shown the drawing), in which only four internal elements are used for assessment of the direction.
  • the other two elements are completed with 50 ⁇ , and are used to homogenize the characteristics of individual elements.
  • Each single pole has a reflector in the shape of half way tube with a diameter of half a wavelength. On one hand the reflector results in a greater effect on the direction, and on the other hand, the connection of elements is minimized. Thus, good fitting and disconnection is achieved. Both values are at about ⁇ 17 dB.
  • the reception model is parameterized by the measured coupling matrix of our antenna group A and the amplification factors of the analog input levels determined by a networking catalyst. Since the occurring compensation of the medium is not known in advance, it is regarded as a variable. The results of the four algorithms applied in this model can be seen in FIG. 7 .
  • NC Unitary ESPRIT appears to be slightly weaker than the ESPRIT and Matrix Pencil, as far as compensation of the medium is below 10 kHz.
  • One possible reason for this is that the accuracy of NC Unitary ESPRIT is dominated by non-homogenous amplification of the input levels (see FIG. 5 ), resulting in RMSE of 0.7°.
  • ESPRIT and Matrix Pencil are more reliable with RMSE of 0.3°.
  • the high compensation of the medium is the limiting factor for ESPRIT, Matrix Pencil and MUSIC, while NC Unitary ESPRIT here shows a constant accuracy of assessment.
  • MUSIC results in values above 10° RMSE in all values of the compensation of the medium and thus appears to be suitable only for special applications.
  • ADS-B messages contain the found position of the airplanes via GPS on board, they are well suited for reference in assessing the direction.
  • 2000 extended squitter ADS-B messages from S mode were collected.
  • the four algorithms were tested with this data set.
  • the results of ESPRIT and NC Unitary ESPRIT are shown in FIG. 8 and FIG. 9 .
  • NC Unitary ESPRIT has to show a RMSE value with 4° lower.
  • MUSIC and Matrix Pencil based on their less reliability, appear to be suitable for special applications in comparison to the compensation of the medium.
  • FIG. 10 shows the determination of the position of an airplane by crossing arrows, based on the individual results from the estimation of the direction of several devices of antenna groups.
  • the central processing unit GCPU calculates the position of the airplane on the basis of direction angles given by individual groups as the point of connection of the corresponding lines, respectively. surfaces (of FIG. 10 for reasons of simplicity only lines are marked, in fact, however, by consideration the azimuth and elevation, the relevant planes are obtained, which are generally curved). For the calculation, methods known by specialists may be used.
  • FIG. 11 and FIG. 12 show improvements in the estimation of the direction by means of calibration.
  • FIG. 11 shows the error in estimating the angle of falling (DOA: Direction of Arrival) to the angle of falling in the use of ESPRIT, here based on 14 222 received ADS-B messages from the airspace.
  • DOA Direction of Arrival
  • the upper part of the diagram shows the results for the uncalibrated case, the lower part—the calibrated case.
  • FIG. 12 shows the histogram uncalibrated (left) and calibrated (right) case in the use of ESPRIT based on the 11642 received ADS-B messages from the airspace, in which the angles are falling are in the range of 45° to 135°.
  • FIG. 11 and FIG. 12 show a systematic reduction of error compared to the uncalibrated case. While here ESPRIT in the uncalibrated case gives another error (RMSE: effective value of the angular error) of about 6°, then this in case of calibration is significantly improved to 2.1°, i.e. nearly one third. In NC Unitary ESPRIT in this use, in the uncalibrated case, an accurate assessment of the direction is achieved. But here also one more visible improvement is achieved by the calibration. The error is reduced from 1.6° to 1.08°. The accuracy of estimation of the direction can be further be improved, for example by using special measuring airplanes for calibration, which give reliable reference signals, reliable data for the position, respectively.
  • RMSE effective value of the angular error
  • calibration can be used also for taking into account effects such as aging of components (generally long-term), temperature or moisture (generally faster and more often fluctuating) or wind power which, by vibrations. can change the positioning of the beam and the beam formation of the group.
  • the use of measurement flights for calibration is more suited for calibration against aging (e.g. every 1-3 years), calibration using ADS-B messages or for supplementing information on the control of the airspace (e.g. primary radar); it generally can be done more frequently and makes calibration possible with view to the temperature and humidity.
  • Various scenarios for the preparation of calibration matrices and storing them can be considered and, depending on the current corresponding parameters, the relevant matrix can be selected.
  • the appropriate sensors e.g. temperature, humidity, wind
  • the development of these devices is possible and its purpose is creating cost-effective devices and their use, where devices are formed in a way that it is not possible to take into account short-term fluctuating parameters such as temperature and humidity, but generally only long-term effects like aging are taken into account.

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  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Radar Systems Or Details Thereof (AREA)
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EP2247960A1 (de) 2010-11-10
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DE102008010882A1 (de) 2009-09-03
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